Recovery of cyclohexanone oxime



United States Patent RECOVERY OF CYCLOHEXANONE OXIME Bernard H. Nicolaisen, Kenmore, and Samuel A. Riccardi, Grand Island, N. Y., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Application August 5, 1954 Serial No. 448,139

Claims. (CL 260-566) This invention relates to improvements in the manufacture of cyclohexanone oxime. More particularly, the present invention is concerned with a process for the recovery of cyclohexanone oxime from solution in an organic solvent.

In the manufacture of cyclohexanone oxime according to one procedure, nitrocyclohexane in its aci-nitro form is partially reduced to the oxime by means of hydrogen sulfideor other sulfides including, for example, ammonium sulfide, sodium sulfide or sodium hydrosulfide, in an acid, aqueous solution. The oxime is then recovered from the aqueous reaction medium by extraction with a suitable water-immiscible, organic solvent, usually a hydrocarbon solvent, for example, petroleum ether, hexane, heptane, toluene, benzene, or cyclohexane. A particularly advantageous process for the hydrogen sulfide reduction and extraction is described in BernardH. Nicolaisen and James B. Ol-Iara application Serial No. 448,088, filed August 5, 1954.

In the sulfide reduction, considerable amounts of sulfur and sulfur compounds are formed. The free sulfur is largely in a finely divided form which is difficult to filter. In addition, organic sulfur compounds of several types appear to be formed as by-products of the reduction. Some of these sulfur compounds are relatively volatile materials and may be distilled overhead with little or no decomposition. Others of these compounds are solids which precipitate during processing in the form of filterable solids. Still others may be obtained as resinous composi tions of high sulfur content. These sulfur compounds or their precursors to a large extent are extracted with the oxime from the aqueous reduction medium and are in solution with the oxime in the extracting solvent. The extract also contains cyclohexanol, cyclohexanone and unreacted nitrocyclohexane. The recovery of cyclohexanone oxime is difficult because of the numerous components present in the extract.

Solutions of the oxime in other solvents, for example, cyclohexanone and nitrocyclohexane, are suitable for-use in the process of the present invention. For example, cyclohexanone oxime can be prepared by the interaction ofcyclohexanone with .hydroxylaminehydrochloride or sulfate in the presencejof an'inorganic base such as caustic orsodium carbonate. At room temperature the oxime precipitates as a solid which can be removed by filtration and, forthe purposes of the present invention, taken up in a suitable solvent such as cyclohexane, petroleum ether or benzene. Alternatively, the slurry of precipitated oxime in water can be extracted with the organic solvent and the extract treated according to the process of the present invention. Solutions of sodium hydroxylarninedisulfonate, prepared from sodium nitrite and sodium bisulfite, or hydroxylamine-O-sulfonic' acid can be substitutedfor the 'hydroxylamine salt.. cyclohexanone. oxime .the oxime is effected in this operation.

can also be produced by the reduction of nitrocyclohexane with zinc dust and acetic acid. The reduction mixture can be neutralized and extracted with a suitable organic solvent to produce a solution suitable for use according to the present invention. Catalytic hydrogenation of nitrocycl-ohexane, for example, by the process of U. S. Patent 2,638,482, produces cyclohexanone oxime., In this process ammonia is used as a source of hydrogen. The reduction mixture can be evaporated and the residue taken up in benzene, cyclohexanone or unreacted nitrocycl'ohexane. Any of these solutions of the oxime are suitable for use according to the process of the present invention. Solutions of cyclohexanone oxime can also be obtained by extracting the hydrogenation products of nitrocyclohexane where hydrogen itself is used as the reducing agent. These hydrogenati-ons can also be carried out in 'cyclohexane or other solvents to provide solutions suitable forus'e according to the present invention.

The separation of the cyclohexanone oxime from solution in an organic solvent in sufliciently pure condition for further use, especially for rearrangement to caprolactam, is the primary purpose ofthe present invention. In addition, it is advantageous when the oxime is obtained by reduction of nitrocyclohexane, to recover unreacted nitrocyclohexa'ne in order to recycle it to the reduction step for eventual conversion to oxime. To be economical it is further desirable to recover and recycle any solvents used in the process. It is a further difiiculty in the recovery of the oxime from the organic extract that in the presence of water, especially acidic solutions and especially at temperatures above 30 C. and up to C., hydrolysis of oxime proceeds rapidly and yields of the product are markedly reduced. The oxime is hydrolyzed primarily to cyclohexanone and hydroxylamine which add to the difiiculty of separating purified oxime. Also, in commercial processing it is difficult to avoid metallic contamination of the oxime due to corrosion of equipment, and it is advantageous to remove these contaminants before the oxime is satisfactory for further treatment.

The present invention provides a method for processing such extracts for the recovery in high yields of the oxime, substantially free from objectionable sulfur, sulfur compounds, metallic compounds, and other -by-products, and for the recovery of unreacted nitrocyclohexane for recycle. Generally, the present invention comprises transferring the oxime from the extracting solvent to an aqueous phase by treating witha dilute, aqueous, strong mineral acid to convert the oxime to a water-soluble salt of the acid with subsequent recovery of the oxime from the aqueous solution by neutralization of the aqueous phase with a suitable base to a pH of about 4.5 to 7.5 in the presence of a water-immiscible organic solvent. The oxime is then utilized in solution in the resulting organic extract or separated therefrom for further processing.

In the initial step of this process, cyclohexanone oxime in solution in a water immiscible organic solvent, which may conveniently be identified as the first organic solvent, is converted to a water-soluble salt by means of extraction with a dilute, aqueous, strong mineral acid. The oxime in the form of its salt dissolves in the aqueous acid While nitrocyclohexane and, when the oxime was produced by a sulfide reduction, part of the by-product sulfur compounds remain in the organic layer. Considerable proportions of the sulfur-containing components also dissolve in the aqueous phase; however substantial purification of In the acid extraction any dilute, aqueous, strong mineralacid can be used, e. g, sulfuric, hydrochloric, or

3 phosphoric acids may be employed. Sulfuric acid is preferred'becau'seit' is" readily available "at low"cost"'ai1d is effective. In addition, the resulting cyclohexanone oxirne sulfate is readily soluble in water and is thoroughly extracted in a single treatment. The concentration of 5 the mineral acid utilized can be between about 5 and 50% based upon the total weightof the-water and acid Sub: stantially lower concentrations: increase theproh'ability bf J hydrolysis and lower the productivkapa'citybf quip; f ment. j-Acid having 'a" concentration of about to %10 H SO4'is particularly advantageous in avoiding hydrolysis and in providing a relativly'large 'aino'untiof diluent-water forheat absdrptiorito aid in temperature control'ili Following the'initial' acid treatmen't'of the 'iir'e's'e'ntpr'oj'c I ess; theaqueous'acidextract containinglthe" oxiifie-in .15 solutionas a'salt'is treated promptly foriecov'c'ry' of the oxime.-- In "this "step a water=imniiscibleorganic "solvent," conveniently'identified"as thes'ec'ondorganic solven'hfi's addedand the mixture is neutralized'b'y"theiaddition of ammonia to a pHof about4z5" 167.5? Oxirheis' libiated20 from its "salt and passes'fintotheforganic' 'Iay'er whereit is 7 removedfr'om" contact"with*"iar'ge' proportions'of Water. and thus is notsubject to hydro' lysi's.""Also,in this step" of theprocesmhost of the sulfur'compounds,'if present; which wereextracted" by the 'acid' in' the'finitial treatinent;" remainin' the 'aqueousacid and the oxime is furtherpurh tied in this respect. iron or other metalliccoritaininaiits are precipitated and are readily"removedbyanysuitable means i' e. g. simple filtrationor settling of the organic extracti By1ieutralizihg to a pI-I'of about 4.5 to 7.5 and preferably -to about 6, the oxime is substantially som pletelyrec'overed' as a s'olution in thesecond organic so vent; J musamsaar of organic solvent'employfedcan vary"; f howeverf'during' iieutraliiation there's'houhi be "enough-" solvent'pre'se'n'tat all times-to eitec't solution of the'oxi'me as itis liberatedtr'om-"its-watersoluble salt: After 'removing precipitated metal "hydroxides, -suitably by aura: tion, theYpurified oxim'e can be recovered-by distillation of the second 'brganic solventor the solutioncan be used directlyfe. g. for rearrangement-ofthe oxime' to capr0'-- 40 lactam: In eithercase---the -recovered solvent can be recycled to the extractiorr'step."

In this neutralization step 'of our process the use of ammonia as thebase to precipitate the free oxime has severaladvantages.--= It low 'in costand is easily intro duced as gaseous-or aqueousammonia. Its heat of neu tralization is less thaii that 'o'f most other" bases suchas caustici However,-"sincer it is 'a stroriger base than the'------ oxime "and a weaker base than cyclohexylamine and other amine-by-products of the r'educti'oii} it. releases the 'oxinie 5.0 thoroughly from the'aque'ous solu'tion at atpH- of about 4.5a: 7.5 While avoiding piecipitation of amine'by-products. Furthermore, the metallic 'impu'r'ities precipitate froin'thetnixture and theh'areremovedby suitable means, for 'example; simple'filt'r'ationflto produce high quality oxime. Aqueous solutions of other alkaliesincludingthe-' alkali and alkaline earth metal-hydroxides ahd carbonates introduce the dangerof over-alkalizing by locally high concentrations of caustic. .Meansmust be pl'0\'-idd f0l -"-f removing-their high-heat of' neutralizatiom When the aqueoussolution is properly neutralized with ammonia' to a pH of about 6,: and fi1tered;=:oximei is substantially cornpletelyrecovered in the' forr'nuof an organic solutic'n of the oxime; 1

To recover any remainingcoxime in the aqueous'layer, it is advantageously re-extractedl-with' a2suitable 'solvent,t= fori'example, cyclohexane,- -to recover .as 'much oxim'e-fias possible "before discarding" the aqueous salt solutio'ml The salt-solution. is? then discharged to -Waste1or workedinp to lay-product ammonium .sulfate-.--' :The organic'isolution of o oxime' is suitablyi combined with ithe princi'p alesolution' of K oxime: I

Any water-immiscible organici solveritslrforatheeoximeh't can housed-1 in the preparationof theiiinitiali solutionor in the extraction'of the-aqueous saltzsolutionmlt impair-2x76 ticularly advantageous to use cyclohexane in both extractions"since'"it' is relatively low boiling compared with" any equipment" for handling a. plurality-of solvents." Cyclohexane is usually Tconvenientlyavailable sinceit is used. as starting material for the manufacture of nitrocyclohexane as the first s'tep of an integrated proc'ess. Other solvents and preferably hydrocarbons such as benzene, toluene, hexane, heptane or narrowcutlow-boiling petroleum fractions can be employed but they do not have the advantageous combination of solvent power, volatility, low solubility forwater and low solubility in water'vof cyclohe'xa'ne... Cyclohex'ane is further advantageous in.

its .'stabili'ty"to 'hot sulfuric acid when it is desired to charge the 'oximesolution dir'ectly'to a rearrangement mixture.

The first organic solvent layer derived from the dilute," aqueous 'acidtreatinent i's" substantially-free from cyclo-" hexanone"oxim"e and is advantageouslytreated forv the recovery'of nitrocyclohexane andisolvent, both of which. can.berecycledl'"iWherethe'oximesolution is obtained by *a" sulfide'i eduction 'of asaltof nitrocyclo'hexane, the organicfsblutioh"canrbe "advantageously extracted with aqu'eott's"cau'sticjfor? example, about"10% NaOI-Il The aqueousalkaline' 'extr'ac't'and solvent layers are" then sepa rated;"for"'exainple; in acontinu'ous separator. The alka linee'xtr'act' of nitrocyclohexaneis recycledand canbe mixedw'ith"thesodiurninitrocyclohexane solution obtained by "alkaline'extractiomof the nitration mixture forcharg ing to the" reductiohoperation' in the process of Bernard H. Nicolaisen and James B. OHara application, Serial Nolf448;088.'" h

After' 's'eparation' of thetalkalineextractof sodium nitrocycloh'exaneg' the undissolved organic 'solvent layer is treated-Torthe recovery "of-solvent and'other products. It may'ybe *distilled; for*exam'ple, in a distilling section which may comprise a continuous-still, orone or more bat'ch vstills. Recovered-solvent is advantageously utilized for thextractiomofgthe aqueous-salt solution from the"; oxi'tne" recipitation step or for the'extractionof the purged reduction liquor of the process of Bernard H. Nicolaisen Where the" oxime is obtained by the hydrogenation of nitrocyclohexane'and -where both' the first and'second sol-" vents"-are--the-same;-the 'organic solution'from the aqueous acid extraction can -be"-'recycled in whole'or impart to the reduction operation. maven-er aportion ofthe solution for the separate-recovet-y of nitrocycloh'exane andsolvent. Where the secwill be nece'ssatys Thenitrocyclohexane can be extracted by' cau'sti'c as described above and recovered from the caustic extract by acidification: --The nitrocyclohexane and solveiit 'can be further purified by' distillation or the solotion can be -'sep arated' -by distillation without the caustic F extractio'nt Boththe nitrocyclohexane and solvent are suitably recyeledzc specific systents for eifecting theprocess'of the present invention; can' itake manyi'forms' but' as-an example the proeessimaybe'performed in the following manner: A

Th roxirri'egtifor example :in cyclohexan'esolvent, obi-" tainedr iby thez'extraction of-the'productr-from thera'cid, aqueouwsulfide-reduction of nitrocyclohexane usually Con-. 3 taiuszzcyelohexanonc roximeuimreducedrnitrocyclohexanetas;

esidual sulfur-containing 'by-products' It is sometimes desirable to by product organic sulfur compounds and cyclohexanone. The solutionmay contain about of cyclohexanone oxime but this amount is not critical. The oxime solution is extracted with dilute aqueous sulfuric acid, for example, about 10% H 80 The operation may comprise thorough mixing and settling in a separator. Alternatively, a continuous counter-current packed extracting column may be used. The solvent, substantially free from oxime but containing other original components of the solution is separated as a supernatant layer and treated for further recovery of its components. The lower layer of aqueous acid solution of cyclohexanone oxime sulfate is separated and transferred to another vessel, suitably a mixer, into which fresh solvent and anhydrous ammonia gas are introduced until the layer reaches a pH of about 6. The heat generated as the sulfuric acid is neutralized raises the temperature of the mixture to about 75 and the oxime dissolves in the solvent. Provision should be made for the removal of excess heat by use of a jacketed kettle or heat exchanger or both. Alternatively the excess heat may be removed by providing for refluxing the cyclohexane or other solvent used. The cooled heterogeneous mixture of cyclohexanone oxime solution and aqueous liquor is transferred to a separator and the supernatant oxime-containing layer is removed. The separated oxime solution after filtration may contain minor proportions of water and salt but it is suitable without further treatment for rearrangement by contact with concentrated sulfuric acid to form caprolactam. Alternatively it may be dried, distilled or otherwise further treated when the oxime is desired as a pure product.

The aqueous salt solution separated from the neutralization operation may contain minor proportions of entrained or dissolved cyclohexanone oxime. It is advantageous therefore to re-extract the aqueous salt solution with an organic solvent to recover the oxime. For example, cyclohexane may be used. The extract can be used as the solvent for extraction of the oxime from the aqueous reduction liquor as described in the process of Bernard H. Nicolaisen and James B. OHara application, Serial No. 448,088. Alternatively the extract may be returned to the neutralization vessel. In addition, the separated salt solution may be mixed with the purge or aqueous reduction liquor of the process of that application and both of these materials may be extracted simultaneously before discarding the aqueous portion.

The process of the present invention may be efiected continuously or batchwise and is further described in the following specific example which is not to be considered limiting.

Example Cyclohexanone oxime was removed from a cyclohexane extract of a hydrogen sulfide-nitrocyclohexane reduction mixture by extracting with aqueous sulfuric acid. The mixture was pumped to and from a tank to mix the liquids. Oxime solution was charged at the rate of 12 parts per hour, 95% sulfuric acid at 1.6 parts per hour, water at 4.3 parts per hour and recycle ammonium sulfate solution at the rate of 6.3 parts per hour. The contents of the tank overfiowed continuously to a decanter separating the oxime-free organic layer and an aqueous oxime sulfate solution. The latter was charged with cyclohexane to a stirred vessel cooled by a water jacket. Anhydrous ammonia was dissolved at the rate of 0.61 part per hour in 2.5 parts per hour of water, cooled and mixed with the oxime sulfate solution. The overflow was separated in a decanter into an aqueous ammonium sulfate solution and a cyclohexane solution. The aqueous stream during most of the run had a pH between 6 and 8, averaging about 6.1. The cyclohexane solution, amounting to about 6.3 parts per hour and containing about 9% of oxime was filtered and charged to a rearrangement operation. The bulk of the aqueous ammonium sulfate solution was recycled to the acid extraction step and a small proportion was extracted to remove any remaining oxime and then discarded. Ammonium sulfate is separated as a by-product from this solution.

We claim:

1. A method for extracting cyclohexanone oxime from solution in a first water immiscible organic hydrocarbon solvent, said solution containing contaminants, which comprises contacting the said solution with a dilute, aqueous, strong mineral acid to form a water soluble salt of the oxime, separating the resulting aqueous phase containing the water soluble salt and neutralizing the separated aqueous phase by the addition of ammonia to a pH of about 4.5 to 7.5 in the presence of a second water immiscible organic hydrocarbon solvent while efiecting solution of the oxime in the said second solvent, said solution of oxime in the second solvent being substantially free of said contaminants.

2. The method according to claim 1 in which said second organic solvent is cyclohexane.

3. The method according to claim 1 in which both the first and second organic solvents are cyclohexane.

4. A method for separately recovering cyclohexanone oxim-e and nitrocyclohexane from solution in a first water immiscible organic hydrocarbon solvent, said solution containing contaminants, which comprises contacting the extract with a dilute, aqueous, strong mineral acid to form a water soluble salt of the oxime, separating the resulting aqueous phase containing the water soluble salt from the non-aqueous phase containing nitrocyclohexane, recovering nitrocyclohexane by caustic extraction from the non-aqueous phase and neutralizing the separated aqueous phase by the addition of ammonia to a pH of about 4.5 to 7.5 in the presence of a second water immiscible organic hydrocarbon solvent while effecting solution of the oxime in the said second organic solvent, said solution of oxime in the second solvent being substantially free of said contaminants.

5. A cyclic and continuous method for separately recovering cyclohexanone oxime and nitrocyclohexane from solution in a first water immiscible organic hydrocarbon solvent, said solution containing contaminants, which comprises contacting the said solution with a dilute, aqueous, strong mineral acid to form a water soluble salt of the oxime, separating the resulting aqueous phase containing the water soluble salt from the non-aqueous phase containing nitrocyclohexane, recovering nitrocyclohexane by caustic extraction from the non-aqueous phase, recycling the caustic extract to a reduction operation effective to form additional cyclohexanone oxime, recycling the first organic solvent to form the solution of cyclohexanone oxime, separating the aqueous acid phase containing the water soluble salt of cyclohexanone oxime and neutralizing the separated aqueous phase by the addition of ammonia to a pH of about 4.5 to 7.5 in the presence of a second water immiscible organic hydrocarbon solvent while effecting solution of oxime in the solvent, said solution of oxime in the second solvent being substantially free of said contaminants, recovering oxime from the second organic solvent and recycling the second organic solvent to the neutralization step.

6. A method for extracting cyclohexanone oxime from a water-immiscible organic hydrocarbon solvent extract of an aqueous sulfide reduction of nitrocyclohexane to cyclohexanone oxime which comprises contacting the extract, said solution containing contaminants, with a dilute, aqueous, strong mineral acid to form a water-soluble salt of the oxime, separating the resultnig aqueous phase containing the water-soluble salt, and neutralizing the separated aqueous phase by the addition of ammonia to a pH of about 4.5 to 7.5 in the presence of a water-immiscible organic hydrocarbon solvent while effecting solution of the oxime in the solvent, said solution of oxime in the second solvent being substantially free of said contaminants. 

1. A METHOD FOR EXTRACTING CYCLOHEXANONE OXIME FROM SOLUTION IN A FIRST WATER IMMISCIBLE ORGANIC HYDROCARBON SOLVENT, SAID SOLUTION CONTAINING CONTAMINANTS, WHICH COMPRISES CONTACTING THE SAID SOLUTION WITH A DILUTE, AQUEOUS STRONG MINERAL ACID TO FORM A WATER SOLUBLE SALT OF THE OXIME, SEPARATING THE RESULTING AQUEOUS PHASE CONTAINING THE WATER SOLUBLE SALT AND NEUTRALIZING THE SEPARATED AQUEOUS PHASE BY THE ADDITION OF AMMONIA TO A PH OF ABOUT 4.5 TO 7.5 IN THE PRESENCE OF A SECOND WATER IMMISCIBLE ORGANIC HYDROCARBON SOLVENT WHILE EFFECTING SOLUTION OF THE OXIME IN THE SAID SECOND SOLVENT, SAID SOLUTION OF OXIME IN THE SECOND SOLVENT BEING SUBSTANTIALLY FREE OF SAID CONTAMINANTS. 